1. Field of the Invention
The present invention relates to a hydroxygallium porphyrazine derivative mixture and an electrophotographic photoconductor.
2. Description of the Related Art
Conventionally known photoelectroconductive materials of photoconductors used in electrophotography are roughly classified to inorganic photoelectroconductive materials and organic photoelectroconductive materials. In general, “electrophotography” refers to a so-called Carlson process which is an image forming process where a photoconductor containing such photoelectroconductive materials is first charged in the dark through, for example, colona discharge; then the photoconductor is imagewise exposed to light so that charges only in the light-exposed portion are selectively dissipated to obtain a latent electrostatic image; then the latent electrostatic image is developed with a toner containing a polymer and a colorant such as a dye or pigment to form a visible image. Photoconductors containing organic photoelectroconductive materials superior to those containing inorganic photoelectroconductive materials in terms of selectivity in photoconductive wavelength regions, film formability, flexibility, film transparency, mass productivity, toxicity and cost. Thus, currently, most of the photoconductors use organic photoelectroconductive materials. Also, photoconductors repeatedly used in such electrophotography and other similar processes are required to be excellent in electrostatic characteristics such as sensitivity, receptive potential, potential retentability, potential stability, residual potential and spectral response.
In recent years, information processing system devices employing electrophotography have remarkably been developed.
In particular, printers employing a digital recording method where information is converted to digital signals which are recorded using light, have remarkably been improved in print quality and reliability. This digital recording method is applied to not only printers but also commonly used copiers, and so-called digital copiers have been developed. Furthermore, various information processing functions are added to this digital copiers, and thus their demand is expected to be increased more and more in the future.
Photoconductors for responding to such a digital recording method have been required to have different characteristics from those required for a conventional analog recording method. For example, at present, a light source mainly used is a small, inexpensive, highly reliable laser diode (LD) or light emitting diode (LED). The wavelength region of light emitted from LD often used currently falls within the near-infrared light region, and the wavelength of light emitted from LED is longer than 650 nm. Therefore, in addition to the above requirements, electrophotographic photoconductors are required to have high sensitivity from the visible light region to the near-infrared light region.
In view of this, the following materials have been proposed as photoelectroconductive materials for used in digital recording: squarylium dyes (see Japanese Patent Application Laid-Open (JP-A) Nos. 49-105536 and 58-21416), triphenylamine trisazo pigments (see JP-A No. 61-151659) and phthalocyanine pigments (see JP-A Nos. 48-34189 and 57-148745). In particular, phthalocyanine pigments, which are tetraazaporphyrin derivatives, have a photoconductive wavelength region in a longer wavelength region and high photosensitivity. They can be varied in characteristics depending on the types of the central metal and the crystal form, and have actively been studied as a photoelectroconductive material for digital recording. Conventionally known phthalocyanine pigments exhibiting good sensitivity include ε-type copper phthalocyanine, X-type metal-free phthalocyanine, τ-type metal-free phthalocyanine, vanadyl phthalocyanine and titanyl phthalocyanine.
JP-A Nos. 64-17066, 03-128973 and 05-98182 have proposed high-sensitive titanyl phthalocyanine pigments. These titanyl phthalocyanine pigments have the maximum absorption of 700 nm to 860 nm as a spectral wavelength region, and show remarkably high sensitivity to light emitted from a laser diode. However, when the titanyl phthalocyanine pigments described in the above patent literatures are used in electrophotographic photoconductors, the electrophotographic photoconductors exhibit sufficient sensitivity but still pose many problems in practical use such as decrease in chargeability caused by repeated fatigue and large variation in sensitivity depending on the temperature and humidity (see Y. Fujimaki, Proc. IS & T's 7th International Congress on Advances in Non-Impact Printing Technologies, 1, 269 (1991)).
Japanese Patent (JP-B) No. 3123185 discloses a chlorogallium phthalocyanine pigment for a photoelectric conversion material. JP-B No. 3166293 discloses a V-type hydroxygallium phthalocyanine pigment for a photoelectric conversion material, which has strong diffraction peaks at Bragg angles (2θ±0.2°) of 7.5°, 9.9°, 12.5°, 16.3°, 18.6°, 25.1° and 28.3° in the X ray spectrum. These gallium phthalocyanine pigments also have practical sensitivity even in the near-infrared region. Although they are lower than the above-described titanyl phthalocyanine pigments in photosensitivity, the dependency of their photosensitivity on the humidity is lower than that of the titanyl phthalocyanine pigment (see K. Daimon, et al.: J. Imaging Sci. Technol., 40, 249 (1996)). However, these gallium phthalocyanine pigments also pose problems such as decrease in chargeability and increase in residual potential (decrease in sensitivity) caused by repeated fatigue.
JP-B Nos. 2637487 and 2637485 disclose porphyrazine pigments each having a heterocyclic ring such as pyridine or pyrazine. Japanese Patent Application Publication (JP-B) No. 03-27111, and JP-B Nos. 4293694 and 4419873 describe that mixtures of phthalocyanine and other porphyrazine pigments are useful for a photoelectroconductive material. However, electrophotographic photoconductors containing these mixtures do not satisfactorily satisfy the above requirements for electrophotographic photoconductors in terms of sensitivity in the visible light region and the near-infrared light region, decrease in chargeability and increase in residual potential caused by repeated fatigue, as well as large variation in sensitivity depending on the temperature and humidity.